I went on a long ride today and about the last 5 miles I noticed that the drivetrain was progressively getting stiffer. It's not really bad, but if I throw the pedals backwards when the bike is on the hanger, they don't go very far. It's like something is binding. The components are 105's.

I took the chain off the front crank and it's a bit better, but not much. I took the chain off the rear cassette and it's a little stiff too.

I'm pretty sure I know the answer, and here is what I think it is.

The bike has been ridden a bit over 500 miles since I've had it. It wasn't used for about a year prior to me getting it, however, right before that it was serviced by a LBS. I haven't oiled the chain since I've had it. With all the dirt and grime that I get on myself when I ride, I'm guessing I've neglected the drivetrain for too long. I used to use WD-40, and I read here that it's bad, and I've kept putting off going to the LBS and getting some good chain oil...

Am I probably right? What's the best way to re lube this thing properly, instead of doing what I did back in the day and flip it upside down and spray WD-40 everywhere why I pedal it with my hands? Thanks in advance.